252 CELLULOSE, LIGNIN, ETC. 



rotatory fermentable sugar, so that this method may he adopted 

 for its estimation. Ammonia dissolves it with difficulty, and 

 it undergoes but little change when heated with potash in 

 sealed tubes (§ 115). 



Gelose,^ the gelatinizing constituent of many algse, agrees with 

 lichenin in most of its properties, but is insoluble in ammonio- 

 sulphate of copper, and is less easily converted into sugar. By 

 decomposition Avith dilute acids, arabinose (lactose) is produced in 

 place of the glucose yielded by lichenin. The gelose appears to 

 be accompanied, at least in Sijhserococcus lichenoides, by a carbo- 

 hydrate ^ soluble in dilute hydrochloric acid, but differing from 

 jjararabin (§ 112) in yielding glucose when boiled with an acid. 



§ 246. Wood-gum. — Thomsen^ found that when ligneous tissue, 

 previously exhausted with water, spirit, and very dilute alkali, 

 was macerated Avith caustic soda of sp. gr. 1-1, a substance was ex- 

 tracted, the composition of which he ascertained to be C^H^gOg, 

 and which he named wood-gum. It can be isolated from its 

 solution in soda by acidifying and adding alcohol. When once 

 dried, cold water will not redissolve it ; this is, however, effected 

 by boiling. It is precipitated by basic acetate of lead, is converted 

 into glucose by boiling with a dilute acid, and is not coloured blue 

 by iodine. An alkaline solution is Isevo-rotatory. It differs 

 from lichenin in not possessing the power of gelatinizing, from 

 metarabin in not being dissolved (when dry) by O'l per cent 

 solution of soda. 



A similar substance was obtained by Pfeil* from parenchymatous 

 tissue (agreeing, however, in composition better with the formula 

 ^i2-^220ii> ^ hydrocellulose), by Treffner from mosses, and by 

 Greenish from algse. 



CELLULOSES, LIGNIN, AND ALLIED SUBSTANCES. 



§ 247. Celluloses, etc. — Fr^my and Terrell^ assume that woody 

 tissue is chiefly composed of three different substances, which they 

 distinguish as cellulose, incrusting substance, and cuticular sub- 



^ Compare Morin and Porumbaru, Comptes rendus, xc. 924, 1081, 1880 

 (Year-book Pharm. 120, 121, 1881). 



- Greenish, Archiv d. Pharm. [3], xx. 241. 



3 Journ. f. pract. Chem. [2], xix. 146, 1879 (Year-book Pharm. 99, 1880). 



* Loc. cit. 



^ Journ. de Pharm, et de Chim. vii. 241, 18G8. 



